Feedback-Aided Coded Random Access with Intentional Power Unbalance

In this paper, feedback-aided coded random access (CRA) protocols for grant-free massive access, with and without exploitation of the power domain, are investigated. The developed schemes can support non-instantaneous acknowledgment messages, along with their time resources, with very little penalty in terms of the achieved tradeoff between scalability, reliability, and latency. The new CRA-type protocols rely on waiting slots introduced between consecutive transmissions from the same device to pipeline the feedback reception without degrading the throughput. Their performance can be further enhanced by exploitation of the power domain, in particular by introduction of a deterministic power selection scheme designed for transmission of different packet replicas over a short time window. The system performance is investigated assuming a realistic wireless channel model, a massive MIMO base station, and a realistic processing, via simulation and analysis. The achieved results show that the realistic feedback-aided protocols with deterministic power selection can support 12.8 grant-free users per slot guaranteeing a packet loss rate of 10−4 while a massive MIMO base station equipped with 128 antennas is employed